These studies will identify and characterize key components of the intrinsic genetic program that controls development and function of male germ cells. The approaches currently being applied are to identify genes expressed specifically in male germ cells, use the gene knockout approach to define the roles of the proteins they encode, employ yeast two-hybrid assays and deletion mutagenesis to identify protein-protein interactions essential for development of the male gamete, and prepare antisera to determine the temporal-spatial distribution of specific gene products. Many genes are expressed only in male germ cells and selected genes are being studied that encode proteins whose functions are essential for four novel aspects of gamete development and/or function. (1) GAPDS and PGK2 are enzymes in the glycolytic pathway produced by spermatogenic cell-specific genes that are orthologues of those expressed in all other tissues. These enzymes bind to the fibrous sheath, a cytoskeletal structure in the sperm flagellum. (2) AKAP4, AKAP3, and CABYR contain protein kinase A (PKA) protein anchoring sites and also are components of the fibrous sheath. (3) Protamines 1 and 2 are highly basic nuclear proteins that replace histones following meiosis. Sperm lack nucleosomes and the protamines are essential for the high degree of DNA compaction in their haploid nuclei. (4) Cdc20 associates with the cyclosome/anaphase-promoting complex (APC) and is essential for APC-dependent proteolysis of cell cycle proteins in the metaphase to anaphase transition. We have identified speriolin, a novel Cdc20-binding factor in spermatogenic cells that might regulate the function of Cdc20 during meiosis in the spermatogenic cells. The first three groups of genes are expressed exclusively during the post-meiotic phase of spermatogenesis, while the last gene is expressed just prior to this phase. Future studies will determine how paracrine, signal transduction, and genetic pathways contribute to the coordinate expression of these genes in spermatogenic cells.